Real image type variable magnification view-finder optical system

ABSTRACT

A real image type variable magnification view-finder optical system consisting of an objective lens system which comprises a plurality of lens units and has a positive refractive power as a whole, and an eyepiece lens system for allowing observation of an image formed by the objective lens system. At least one of the plurality of lens units comprises two or more lens components and is configured so as to permit varying one or more airspaces reserved between the at least two lens components. This real image type variable magnification view-finder optical system is capable of switching a visual field thereof for a usual photographing mode to another visual field for a panoramic photographing mode.

BACKGROUND OF THE INVENTION

a) Field of the invention

The present invention relates to a view-finder optical system to be usedwith photographic cameras, video cameras and so on, and morespecifically to a real image type variable magnification view-finderoptical system which is suited for panoramic photographing.

b) Description of the prior art

In the recent days, people are fond of photographs taken on films havingslenderness ratios which are obtained by trimming the conventional filmsizes (for example, 36 mm by 22 mm). As an example of these photographstaken on the films having such slenderness ratios, there is known apanoramic photograph which is obtainable by photographing an objectwhile covering an upper portion and a lower portion of a film andenlarging a photographed image of the object at a printing stage thereofso as to elongate a photographed range of the object sideways foremphasizing a wide impression of the photographed image.

Since a field angle of incidence for trimming a film surface is smallerthan a field angle of incidence for photographing an object on a fullsize of the film surface, it was conventionally necessary to narrow apicture plane of a view-finder of a camera having a panoramicphotographing function in conjunction with narrowing of the field angleof incidence so as to maintain a constant field ratio for the panoramicphotographing mode. Accordingly, a range of the visual field withinwhich an object is to be photographed was indicated by using straightlines traced within a frame of the visual field or the picture plane ofthe view-finder was narrowed by shortening a vertical size of the frameof the visual field.

When the range of the visual field within which the object is to bephotographed was indicated within the frame of the visual field,however, a photographer could not judge, so long as he was peepingthrough the view-finder, whether the camera is set in either of thephotographing mode and sometimes misunderstood a range within which theobject is to be photographed since the picture plane of the view-finderhas a size remaining unchanged between a usual photographing mode andthe panoramic photographing mode. In this case, the view-finder opticalsystem has another defect that it permitted the photographer observingportions of the visual field which were not to be photographed, therebyhindering the trimming operation to be performed by the photographer. Inthe other case where the picture plane of the view-finder is narrowed byshortening the vertical size of the frame of the visual field, incontrast, an image observed through the view-finder in the panoramicphotographing mode gave a contracted impression, contrary to the wideimpression, whereby a photographed image often gave an impression whichwas often different from that of the image observed at a photographingstage.

In order to correct the defects described above, there have hithertobeen contrived methods to enlarge sizes of picture planes of visualfields by enhancing magnifications of view-finders in the panoramicphotographing mode. These methods make it possible to enlarge thepicture planes in conjunction with field angles of incidence ofphotographic lens systems so that images observed through theview-finders gave wide impressions.

As one of the methods for enhancing the magnifications of theview-finders, there is known a method to preliminarily design zoomingcams so as to permit obtaining vari-focal ratios which are higher thanthose required for the usual photographing mode and perform, atphotographing stages, changes of magnifications for the panoramicphotographing mode after shifting vari-focal lens units.

This method requires using two mechanisms for each view-finder: onemechanism required for shifting a vari-focal lens unit regardless of thephotographing modes; and the other mechanism required for shifting lensunits only in the panoramic photographing mode. As a result, thevari-focal lens unit must be shifted along a complicated locus and anassembly of these two mechanisms has a complicated structure, therebyposing a problem that the mechanisms can hardly be manufactured inpractice.

SUMMARY OF THE INVENTION

A primary object of the present invention, which has been made in viewof the problems posed by the prior art, is to provide a real image typevariable magnification view-finder optical system which has a simplecomposition and permits performing changes of magnifications withoutpreliminarily shifting lens units in the panoramic photographing mode.

According to the present invention, this object is attained by composinga real image type variable magnification view-finder optical system ofan objective lens system which comprises a plurality of lens units andhas a positive refractive power as a whole, and an eyepiece lens systemfor allowing observation of an image formed by the objective lenssystem; and configuring the view-finder optical system so that amagnification of the view-finder optical system is changed from a wideposition to a telephoto position thereof by varying at least one ofairspaces reserved among the plurality of lens units, at least one ofthe lens units comprises two or more lens components and a change of amagnification of the view-finder optical system for trimming of a visualfield thereof is performed by varying an airspace reserved between thetwo lens components or at least one of airspaces reserved among the morelens components.

Now, a preferable formation of the real image type variablemagnification view-finder optical system will be explained below.

First, description will be made of changes of magnifications of theview-finder optical system over an entire zooming range, or a method forvarying a focal length of the objective lens system by changing a focallength of a lens unit which is to be kept stationary in a photographingmode (hereinafter referred to as a fixed lens unit in some cases)without shifting movable lens units.

FIG. 1 is a diagram descriptive of a fundamental concept of the realimage type variable magnification view-finder optical system accordingto the present invention. In this drawing, the reference numeral 1represents an objective lens system which consists of a first fixed lensunit G₁ (to be kept stationary in a photographing mode), a secondmovable lens unit G₂, a third movable lens unit G₃ and a fourth lensunit G₄ composed of a prism which functions to form an intermediateimage of an object on a surface of emergence thereof after reflectingincident rays twice. The reference numeral 2 designates an eyepiece lenssystem which consists of a fifth lens unit G₅ composed of a prismfunctioning to reflect the incident rays twice and a sixth fixed lensunit G₆, and the reference symbol EP denotes an eye point.

In this preferable formation of the view-finder optical system accordingto the present invention which has the composition described above, amagnification of the view-finder optical system is changed by varying afocal length of the first fixed lens unit G₁. An operating principle forchanging the focal length of the first lens unit G, will be describedwith reference to FIG. 2A illustrating a condition of the objective lenssystem 1 before changing the focal length of the first lens unit G₁ andFIG. 2B illustrating another condition of the objective lens system 1after changing the focal length of the first lens unit G₁. Since thefirst lens unit G₁ is kept stationary over the entire vari-focal range,a focal point P_(A) thereof is always constant. Accordingly, an objectpoint for the second lens unit G₂, the third lens unit G₃ and the fourthlens unit G₄ is always located at P_(A), and the object point is imagedat an image point Q_(A). It is therefore possible to change a focallength of the objective lens system 1 from F_(A) to F_(A) ' A bychanging an airspace d_(m1) reserved between the first lens unit G₁ andthe second lens unit G₂ shown in FIG. 2A to an airspace d_(m1) ' shownin FIG. 2B, and changing a focal length of the first lens unit G₁ tothat of a lens unit G₁ ' so as to coincide a focal point thereof withP_(A) while keeping the second lens unit G₂, the third lens unit G₃ andthe fourth lens unit stationary. The magnification of the view-finderoptical system can be varied by changing the focal length of the firstlens unit G₁.

Then, description will be made, with reference to FIG. 3 and FIG. 4, ofan operating principle of the magnification of the view-finder opticalsystem in a case where the first lens unit G₁ is movable. In FIG. 3, thereference numeral 1 represents an objective lens system which consistsof a first movable lens unit G₇, a second movable lens unit G₈ and athird movable lens unit G₉ which is composed of a prism functioning toform an intermediate image on a surface of emergence thereof afterreflecting incident rays twice. The reference numeral 2 designates aneyepiece lens system which consists of a fourth lens unit G₁₀ composedof a prism functioning to reflect the incident rays twice and a fifthfixed lens unit G₁₁, whereas the reference symbol EP denotes an eyepoint.

In case of the view-finder optical system which has the compositiondescribed above, a magnification thereof is varied by changing a focallength of the first movable lens unit G₇. An operating principle forchanging the focal length of the first lens unit G₇ will be describedwith reference to FIG. 4A illustrating a condition of the objective lenssystem before changing the focal length of the first lens unit G₇ andFIG. 4B illustrating another condition of the objective lens systemafter changing the focal length of the first lens unit G₇. Let usrepresent a focal point of the first lens unit G₇ in a given vari-focalposition by P_(B). At this position, an object point P_(B) for thesecond lens unit G₈ and the third lens unit G₉ is imaged at an imagepoint Q_(B). When an airspace d_(m7) reserved between the first lensunit G₇ and the second lens unit G₈ shown in FIG. 4A is varied to anairspace d_(m7) ' shown in FIG. 4B and a focal length of the first lensunit G₇ is changed to that of a lens unit G₇ ' so as to coincide a focalpoint thereof with P_(B), a focal length of the objective lens system 1can be varied from F_(B) to F_(B) ' while keeping a constant airspaced_(m8) reserved between the second lens unit G₈ and the third lens unitG₉. Since the first lens unit G₇ is movable, however, the airspaced_(m7) is not constant as is understood from (d_(m7) ≠d_(m7) '). Amagnification of the view-finder optical system can be changed byvarying the focal length of the first movable lens unit G₇ as well asthe airspace reserved between the first lens unit G₇ and the second lensunit G₈.

Description has been made above of the fact that the magnification ofthe view-finder optical system can be changed by varying a focal lengthof a certain lens unit. Now, a method to vary the focal length of thislens unit will be explained. It is conceivable, as a simplest method tovary a focal length, to exchange a lens unit with another. However, itis necessary for carrying out this method to reserve a space for savingthe lens unit from an optical path, whereby a camera which is to use aview-finder optical system comprising this lens unit will sometimes beenlarged and complicated in mechanical structure thereof. In theview-finder optical system according to the present invention, such alens unit is composed of two or more lens components and a focal lengthof the lens unit is varied by moving these lens components along anoptical axis.

For varying the focal length of the lens unit without exchanging thelens unit with another, it is sufficient to compose the lens unit of twoor more lens components and vary a total focal length of the lenscomponents by moving at least two of the lens components. An operatingprinciple for varying the focal length of the lens unit will bedescribed with reference to FIG. 5A and FIG. 5B. A lens unit shown inthese drawings corresponds to the first lens unit G₁ or G₇ which hasbeen described above. When a focal length of a front lens componentG_(1A) Of the lens unit is represented by f₁, a focal length of a rearlens component G_(1B) is designated by f₂, an airspace reserved betweenthese lens components is denoted by d and a total focal length of thesetwo lens components is represented by f (see FIG. 5A), we obtain thefollowing formula (1):

    1/f=1/f.sub.1 +1/f.sub.2 -d/f.sub.1 f.sub.2, or f=f.sub.1 f.sub.2 /(f.sub.1 +f.sub.2 -d)                                              (1)

When a focal length of the view-finder optical system after changing themagnification thereof is represented by f' and an airspace reservedbetween the lens components after changing the magnification isdesignated by d' (see FIG. 5B), f' is defined as Mf (M: a constant), d'is expressed by the following formula (2):

    d'=[(M-1)/M]·(f.sub.1 +f.sub.2)+d/M               (2)

In the formula (2) mentioned above, the term [(M-1)/M] is a constant andthe term (d/M) is also a constant when d is assumed to be, for example,as 1 mm. Hence, d' is a function of the term (f₁ +f₂).

When f₁ and f₂ have the same sign in the formulae (1) and (2) mentionedabove, i.e., in a case of (f₁ >0, f₂ >0) or (f₁ <0, f₂ <0), the airspaced is largely different from the airspace d', thereby making theview-finder optical system unpractical. When f₁ has a sign which isreverse to that of f₂, it is possible to change the total focal lengthby slightly varying the airspace d, thereby obtaining an advantage forconfiguring the view-finder optical system compact. Accordingly, it isdesirable to configure the front lens component and the rear lenscomponent so that f₁ and f₂ have signs which are reverse to each other,i.e., so as to have relationship of (f₁ >0, f₂ <0) or (f₁ <0, f₂ >0).

When the vari-focal lens unit is composed of two or more lenscomponents, it is possible to change the magnification of theview-finder optical system over the entire zooming range simply byvarying an airspace reserved between the two or more lens components.For moving these two or more lens components for short distances andshortening a total length of the objective lens system, it is sufficientto configure the vari-focal lens unit so as to satisfy the followingconditions (3) and (4):

    (f.sub.1 +d')/(f.sub.1 +d)>1.02                            (3)

    (f.sub.2 +d')/(f.sub.2 +d)>1.02                            (4)

wherein the reference symbol f₁ represents a focal length of the frontlens component G_(1A) of the vari-focal lens unit, the reference symbolf₂ designates a focal length of the rear lens component G_(1B) of thevari-focal lens unit, the reference symbol d denotes an airspacereserved between these two lens components at a low magnification of theview-finder optical system and the reference symbol d' represents anairspace reserved between the lens components at a high magnification ofthe view-finder optical system.

Let us represent a total focal length of these lens components by f. Thecondition (3) is to be adopted in a case of f >0 and (f₁ <0, f₂ >0) or acase of f<0(f₁ >0, f₂ <0). The condition (4) is to be adopted in a caseof f>0 and (f₁ >0, f₂ <0) or a case of f<0 (f₁ <0, f₂ >0).

In each of the cases mentioned above, aberrations will be aggravated dueto f₂ if the condition (3) is not satisfied or aberrations will beaggravated due to f₁ if the condition (4) is not satisfied. Opticalperformance of the view-finder optical system will be remarkablydegraded by the aggravation of the aberrations.

It is desirable that the lens components which are movable toward theside of the eyepiece lens system in the lens unit comprising thevariable airspace have a total focal length whose sign is reverse tothat of a focal length of the lens unit comprising the variable airspacesince the lens components will be large and aberrations cannot becorrected favorably if these focal lengths have signs which are notreverse to each other. Furthermore, use of at least one asphericalsurface in each of the lens units is advantageous for correctingaberrations favorably to certain degrees and shortening of a totallength of the objective lens system.

When the objective lens system consists of three lens units including afirst fixed lens unit and a magnification of the objective lens systemis to be changed by moving lens components disposed in the first lensunit, the objective lens unit should desirably satisfy the followingcondition (5):

    m.sub.2T /m.sub.2W -m.sub.3T /m.sub.3W >0                  (5)

wherein the reference symbol m_(2W) represents a magnification of asecond lens unit at the wide position of the view-finder optical system,the reference symbol m_(2T) designates a magnification of the secondlens unit at the telephoto position of the view-finder optical system,the reference symbol m_(3W) denotes a magnification of a third lens unitat the wide position of the view-finder optical system and the referencesymbol m_(3T) represents a magnification of the third lens unit at thetelephoto position of the view-finder optical system.

As is judged from the condition (5) mentioned above, the second lensunit has a main role for changing the magnification, whereas the thirdlens unit has a role to adjust diopter. If the condition (5) is notsatisfied, it will be impossible to reserve required airspaces among thelens units or compose the objective lens system in practice.

Moreover, it is possible to compose the view-finder optical system so asto permit graduating magnification scale divisions for zoomingoperations at equal intervals or at intervals which are different atdifferent magnification levels. For this purpose, it is necessary to usetwo kind of cams.

The present invention makes it possible to change a magnification of theview-finder optical system so as to be suited for the panoramicphotographing mode by varying an airspace reserved between the lenscomponents of the lens unit consisting of the two or more lens units.When the lens unit is kept stationary so long as a photographing mode isnot switched to the other, it is possible to select a constant airspaceamong the other movable lens units or a constant shape for the cams. Asa result, the real image type variable magnification view-finder opticalsystem according to the present invention has a merit that it can besimple in a mechanical structure thereof.

This and other objects as well as the features and the advantages of thepresent invention will become apparent from the following detaileddescription of the preferred embodiments when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram descriptive of the concept of the real image typevariable magnification view-finder optical system according to thepresent invention when it is configured so as to vary a focal length ofa fixed lens unit;

FIG. 2A and FIG. 2B are diagrams illustrating an operating principle ofthe real image type variable magnification view-finder optical systemwhen it is configured so as to vary a focal length of a fixed lens unit,or conditions of the real image type variable magnification view-finderoptical system before and after respectively the focal length of thefixed lens unit is varied;

FIG. 3 is a diagram descriptive of a concept of the real image typevariable magnification view-finder optical system according to thepresent invention when it is configured so as to vary a focal length ofa movable lens unit;

FIG. 4A and FIG. 4B are diagrams illustrating an operating principle ofthe real image type variable magnification view-finder optical systemaccording to the present invention when it is configured so as to varythe focal length of the movable lens unit, or conditions of the realimage type variable magnification view-finder optical system before andafter respectively the focal length of the movable lens unit is varied;

FIG. 5A and FIG. 5B are diagrams visualizing an operating principle ofan optical system when it is configured so as to vary a focal lengththereof by varying airspaces reserved among lens units, or conditions ofthe optical system before and after respectively the airspaces among thelens units are varied;

FIG. 6 shows development diagrams of optical paths at a wide position, amiddle position and a telephoto position of a first embodiment of thereal image type variable magnification view-finder optical systemaccording to the present invention when it is set in the usualphotographing mode;

FIG. 7 shows development diagrams of optical paths at the wide position,middle position and telephoto position of the first embodiment of thepresent invention when it is set in the panoramic photographing mode;

FIG. 8 shows graphs illustrating aberration characteristics of the firstembodiment of the present invention in the usual photographing modethereof;

FIG. 9 shows graphs illustrating aberration characteristics of the firstembodiment of the present invention in the panoramic photographing modethereof;

FIG. 10 shows graphs development diagrams of optical paths at the wideposition, middle position and telephoto position of a second embodimentof the real image type variable magnification view-finder optical systemaccording to the present invention when it is set in the usualphotographing mode;

FIG. 11 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of the secondembodiment of the present invention in the panoramic photographing modethereof;

FIG. 12 shows curves illustrating aberration characteristics of thesecond embodiment of the present invention in the usual photographingmode thereof;

FIG. 13 shows curves illustrating aberration characteristics of thesecond embodiment of the present invention in the panoramicphotographing mode thereof;

FIG. 14 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of a third embodimentof the real image type variable magnification view-finder optical systemaccording to the present invention when it is set in the usualphotographing mode;

FIG. 15 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of the third embodimentof the present invention when it is set in the panoramic photographingmode;

FIG. 16 shows curves visualizing aberration characteristics of the thirdembodiment of the present invention in the usual photographing modethereof;

FIG. 17 shows graphs illustrating aberration characteristics of thethird embodiment of the present invention in the panoramic photographingmode thereof;

FIG. 18 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of a fourth embodimentof the real image type variable magnification view-finder optical systemaccording to the present invention when it is set in the usualphotographing mode;

FIG. 19 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of the fourthembodiment of the present invention in the panoramic photographing modethereof;

FIG. 20 shows graphs illustrating aberration characteristics of thefourth embodiment of the present invention in the usual photographingmode thereof;

FIG. 21 shows curves illustrating aberration characteristics of thefourth embodiment of the present invention in the panoramicphotographing mode thereof;

FIG. 22 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of a fifth embodimentof the real image type variable magnification view-finder optical systemaccording to the present invention when it is set in the usualphotographing mode;

FIG. 23 shows development diagrams of optical paths at the wideposition, middle position and telephoto position of the fifth embodimentof the present invention when it is set in the panoramic photographingmode;

FIG. 24 shows graphs visualizing aberration characteristics of the fifthembodiment of the present invention in the usual photographing modethereof; and

FIG. 25 shows curves illustrating aberration characteristics of thefifth embodiment of the present invention in the panoramic photographingmode thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the real image type variable magnification view-finder opticalsystem according to the present invention will be described moredetailedly below with reference to the preferred embodiments thereofillustrated in the accompanying drawings.

First Embodiment

FIG. 6 and FIG. 7 illustrate the development diagrams of optical pathsat the wide position, middle position and telephoto position of thefirst embodiment of the real image type variable magnificationview-finder optical system according to the present invention in theusual photographing mode and the panoramic photographing moderespectively. An objective lens system 1 shown in these drawingsconsists of a first fixed lens unit G₁ which has a negative refractivepower as a whole, and is composed of a first lens component G_(1A)having a negative refractive power and a second lens component G_(1B)having a positive refractive power, a second movable lens unit G₂ whichhas a positive refractive power and is movable for zooming, a third lensunit G₃ which has a negative refractive power and is movable forzooming, and a fourth lens unit G₄ composed of a prism which has tworeflecting surfaces and a positive refractive power. An intermediateimage of an object (not shown) is formed by the objective lens systemwithin a visual field frame which is disposed on a surface of emergenceof the fourth lens unit G₄. This intermediate image is observed throughan eyepiece lens system 2 which consists of a fifth lens unit G₅composed of a prism having two reflecting surfaces and a sixth fixedlens unit G₆ having a positive refractive power.

In the usual photographing mode, a magnification of the view-finderoptical system is changed by moving the second lens unit G₂ and thethird lens unit G₃ while keeping the first lens unit G₁ stationary. Inthe panoramic photographing mode, in contrast, a magnification of theview-finder optical system can be changed by varying an airspacereserved between the first lens component G_(1A) and the second lenscomponent G_(1B) of the first lens unit G₁ and moving the first lensunit G₁ so as to vary an airspace reserved between this lens unit andthe second lens unit G₂ for adjustment of diopter while keeping thesecond lens unit G₂, the third lens unit G₃ and the fourth lens unit G₄stationary. In conjunction with switching from the usual photographingmode to the panoramic photographing mode, a visual field frame for theusual photographing mode (not shown) is exchanged with another for thepanoramic photographing mode. In addition, the magnification of theview-finder optical system is changed also by moving the second lensunit G₂ and the third lens unit G₃.

The first embodiment of the present invention features a merit of simplemechanical structure thereof owing to the fact that the magnification ofthe view-finder optical system can be changed to a desired level simplyby moving tile first lens unit G₁ (which is to be kept stationary ineither of the two photographing modes) and varying the airspace reservedin this lens unit without changing locations of the movable lens units.

Numerical data for the development diagrams of the optical paths shownin FIG. 6 and FIG. 7 are listed below. Further, aberrationcharacteristics at the wide position, middle position and telephotoposition in the usual photographing mode are illustrated in FIG. 8, andthose at the wide position, middle position and telephoto position inthe panoramic photographing mode of the first embodiment are illustratedin FIG. 9.

    ______________________________________                                        <Usual photographing mode>                                                    Magnification     0.42˜0.55˜0.73                                  Angle of incidence (2ω)                                                                   49.8°˜38.9°˜28.4°          <Panoramic photographing                                                      mode>                                                                         Magnification     0.50˜0.66˜0.88                                  Angle of incidence (2ω)                                                                   46.2°˜35.9°˜26.0°          Condition (4)     (f.sub.2 + d')/(f.sub.2 + d) = 1.083                        Condition (5)     m.sub.2T /m.sub.2W - m.sub.3T /m.sub.3W = 0.775             r.sub.1 = -134.7637                                                                       d.sub.1 = 1.000                                                                          n.sub.1 = 1.58423                                                                        ν.sub.1 = 30.49                          r.sub.2 = 4.8230                                                                          d.sub.2 = D.sub.1                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.3 = 9.0460                                                                          d.sub.3 = 2.000                                                                          n.sub.2 = 1.49241                                                                        ν.sub.2 = 57.66                          (aspherical surface)                                                          r.sub.4 = 359.1474                                                                        d.sub.4 = D.sub.2                                                             (variable)                                                        r.sub.5 = 11.7341                                                                         d.sub.5 = 3.500                                                                          n.sub.3 = 1.49241                                                                        ν.sub.3 =  57.66                         r.sub.6 = -19.3895                                                                        d.sub.6 = D.sub.3                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.7 = 41.3019                                                                         d.sub.7 = 1.000                                                                          n.sub.4 = 1.58423                                                                        ν.sub.4 = 30.49                          r.sub.8 = 8.3103                                                                          d.sub.8 = D.sub.4                                                             (variable)                                                        r.sub.9 = 7.6460                                                                          d.sub.9 = 20.445                                                                         n.sub.5 = 1.49241                                                                        ν.sub.5 = 57.66                          (aspherical surface)                                                          r.sub.10 = ∞                                                                        d.sub.10 = 1.000                                                  r.sub.11 = ∞                                                                        d.sub.11 = 25.000                                                                        n.sub.6 = 1.49241                                                                        ν.sub.6 = 57.66                          r.sub.12 = ∞                                                                        d.sub.12 = 2.000                                                  r.sub.13 = 17.8899                                                                        d.sub.13 = 3.400                                                                         n.sub.7 = 1.49241                                                                        ν.sub.7 = 57.66                          r.sub.14 = -22.9622                                                                       d.sub.14 = 20.000                                                 (aspherical surface)                                                          r.sub.15 (EP)                                                                 Aspherical surface coefficients                                               Second surface (r.sub.2)                                                      P = 1.0000        A.sub.4 = -0.17361 × 10.sup.-2                        A.sub.6 = 0.22728 × 10.sup.-4                                                             A.sub.8 = -0.26239 × 10.sup.-5                        Third surface (r.sub.3)                                                       P = 1.0000        A.sub.4 = -0.49459 × 10.sup.-3                        A.sub.6 = 0.12656 × 10.sup.-4                                                             A.sub.8 = -0.11763 × 10.sup.-6                        Sixth Surface (r.sub.6)                                                       P = 1.0000        A.sub.4 = 0.12237 × 10.sup.-3                         A.sub.6 = 0.14520 × 10.sup.-5                                                             A.sub.8 = 0.10884 × 10.sup.-8                         Ninth surface (r.sub.9)                                                       P = 1.0000        A.sub.4 = -0.36463 × 10.sup.-3                        A.sub.6 = 0.30412 × 10.sup.-5                                                             A.sub.8 = -0.12085 × 10.sup.-6                        Fourteenth surface (r.sub.14 )                                                P = 1.0000        A.sub.4 = 0.79267 × 10.sup.-4                         A.sub.6 = -0.57040 ×  10.sup.-6                                                           A.sub.8 = 0.68501 × 10.sup.-8                         Airspaces at different positions                                              ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                        <Usual photographing mode>                                                    Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              1.0000         1.0000  1.0000                                          D.sub.2                                                                              19.8269       14.3983  9.3809                                          D.sub.3                                                                              7.5305        10.4829  15.4403                                         D.sub.4                                                                              2.8556         5.3318  5.3917                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        <Panoramic photographing mode>                                                Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              2.6456        2.6456   2.6456                                          D.sub.2                                                                              12.6934       7.2648   2.2475                                          D.sub.3                                                                              7.5305        10.4829  15.4403                                         D.sub.4                                                                              2.8555        5.3318   5.3917                                          ______________________________________                                    

Second Embodiment

FIG. 10 and FIG. 11 show development diagrams of optical paths at thewide position, middle position and telephoto position of the real imagetype variable magnification view-finder optical system preferred as thesecond embodiment of the present invention; FIG. 10 illustrating theoptical paths in the usual photographing mode and FIG. 11 illustratingthe optical paths in the panoramic photographing mode. The view-finderoptical system preferred as this embodiment consists of an objectivelens system 1 and an eyepiece lens system 2. The objective lens system 1consists of a first fixed lens unit G₁ which is composed of a first lenscomponent G_(1A) having a negative refractive power and a second lenscomponent G_(1B) having a positive refractive power, and has a negativerefractive power as a whole, a second movable lens unit G₂ which has apositive refractive power and is movable for zooming, a third movablelens unit G₃ having a positive refractive power, and a fourth lens unitG₄ composed of a prism which has two reflecting surfaces and a positiverefractive power, whereas the eyepiece lens system 2 consists of a fifthlens unit G₅ composed of a prism which has two reflecting surfaces and asixth fixed lens unit G₆ having a positive refractive power. Though notshown in FIG. 10 or FIG. 11, visual field frames which have sizesmatched with the photographing modes are disposed on a surface ofemergence of the fourth lens unit G₄.

Even when each of the second lens unit G₂ and the third lens unit G₃ iscomposed of a single lens component having a positive refractive power,unlike the first and second lens units used in the first embodiment, thesecond embodiment can provide the effect which is similar to thatobtained by the first embodiment.

Numerical data for the development diagrams shown in FIG. 10 and FIG. 11are listed below. Further, aberration characteristics at the wideposition, middle position and telephoto position in the usualphotographing mode are visualized in FIG. 12 and those at the wideposition, middle position and telephoto position in the panoramicphotographing mode are visualized in FIG. 13.

    ______________________________________                                        <Usual photographing mode>                                                    Magnification     0.42˜0.55˜0.73                                  Angle of incidence (2ω)                                                                   48.7°˜36.3°˜25.9°          <Panoramic photographing                                                      mode>                                                                         Magnification     0.50˜0.66˜0.83                                  Angle of incidence (2ω)                                                                   43.8°˜32.8°˜23.3°          Condition (4)     (f.sub.2 + d')/(f.sub.2 + d) = 1.062                        Condition (5)     m.sub.2T /m.sub.2W - m.sub.3T /m.sub.3W = 0.748             r.sub.1 = -11.5915                                                                        d.sub.1 = 1.000                                                                          n.sub.1 = 1.58423                                                                        ν.sub.1 = 30.49                          r.sub.2 = 8.7806                                                                          d.sub.2 = D.sub.1                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.3 = 16.5152                                                                         d.sub.3 = 2.000                                                                          n.sub.2 = 1.49241                                                                        ν.sub.2 = 57.66                          (aspherical surface)                                                          r.sub.4 = -16.6476                                                                        d.sub.4 = D.sub.2                                                             (variable)                                                        r.sub.5 = 15.4967                                                                         d.sub.5 = 3.500                                                                          n.sub.3 = 1.49241                                                                        ν.sub.3 =  57.66                         r.sub.6 = -27.6468                                                                        d.sub.6 = D.sub.3                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.7 = -39.8150                                                                        d.sub.7 = 3.000                                                                          n.sub.4 = 1.49241                                                                        ν.sub.4 = 57.66                          r.sub.8 = -14.1016                                                                        d.sub.8 = D.sub.4                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.9 = ∞                                                                         d.sub.9 = 23.107                                                                         n.sub.5 = 1.49241                                                                        ν.sub.5 = 57.66                          r.sub.10 = ∞                                                                        d.sub.10 = 1.000                                                  r.sub.11 = ∞                                                                        d.sub.11 = 25.000                                                                        n.sub.6 = 1.49241                                                                        ν.sub.6 = 57.66                          r.sub.12 = ∞                                                                        d.sub.12 = 2.000                                                  r.sub.13 = 17.8960                                                                        d.sub.13 = 3.400                                                                         n.sub.7 = 1.49241                                                                        ν.sub.7 = 57.66                          r.sub.14 = -22.9520                                                                       d.sub.14 = 20.000                                                 (aspherical surface)                                                          r.sub.15 (EP)                                                                 Aspherical surface coefficients                                               Second surface (r.sub.2)                                                      P =  1.0000       A.sub.4 = -0.71271 × 10.sup.-3                        A.sub.6 = -0.69719 × 10.sup.-5                                                            A.sub.8 = 0.33408 × 10.sup.-6                         Third surface (r.sub.3)                                                       P = 1.0000        A.sub.4 = -0.24343 × 10.sup.-3                        A.sub.6 = 0.32518 × 10.sup.-5                                                             A.sub.8 = -0.90260 × 10.sup.-7                        Sixth Surface (r.sub.6)                                                       P = 1.0000        A.sub.4 = 0.82557 × 10.sup.-4                         A.sub.6 = 0.86903 × 10.sup.-6                                                             A.sub.8 = -0.22639 × 10.sup.-7                        Eight surface (r.sub.8)                                                       P = 1.0000        A.sub.4 = 0.13461 × 10.sup.-3                         A.sub.6 = -0.18620 × 10.sup.-5                                                            A.sub.8 = 0.36551 × 10.sup.-7                         Fourteenth surface (r.sub.14 )                                                P = 1.0000        A.sub.4 = 0.79267 × 10.sup.-4                         A.sub.6 = -0.57040 × 10.sup.-6                                                            A.sub.8 = 0.68501 × 10.sup.-8                         Airspaces at different portions                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        <Usual photographing mode>                                                    Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              1.0000         1.0000  1.0000                                          D.sub.2                                                                              22.2947       16.2874  9.5672                                          D.sub.3                                                                              1.0000        8.2126   14.3385                                         D.sub.4                                                                              3.2053        2.0000   2.5943                                          ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        <Panoramic photographing mode>                                                Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              2.1336        2.1336   2.1336                                          D.sub.2                                                                              13.7275       7.7202   1.0000                                          D.sub.3                                                                              1.0000        8.2126   14.3385                                         D.sub.4                                                                              3.2053        2.0000   2.5943                                          ______________________________________                                    

Third Embodiment

FIG. 14 and FIG. 15 are development diagrams illustrating optical pathsat the wide position, middle position and telephoto position of the realimage type variable magnification view-finder optical system which ispreferred as the third embodiment of the present invention; FIG. 14showing the optical paths in the usual photographing mode and FIG. 15showing those in the panoramic photographing mode. The view-finderoptical system preferred as this embodiment consists of an objectivelens system I and an eyepiece lens system 2. The objective lens system 1comprises a first lens unit G₁ which consists of a first lens componentG_(1A) having a negative refractive power and a second lens componentG_(1B) having a positive refractive power, and has a negative refractivepower as a whole, the first lens unit G₁ being so arranged that thefirst lens component G_(1A) and the second lens component G_(1B) may bemoved integrally for zooming and an airspace therebetween may be variedwhen the usual photographing mode is changed to the panoramicphotographing mode or when the panoramic photographing mode is changedto the usual photographing mode, a second lens unit G₂ which has apositive refractive power and is to be moved for zooming, and a thirdlens unit G₃ composed of a prism which has two reflecting surfaces and apositive refractive power, whereas the eyepiece lens system 2 consistsof a fourth lens unit G₄ which is composed of a prism having tworeflecting surfaces, and a fifth lens unit G₅ which has a positiverefractive power and is to be kept stationary during zooming. Visualfield frames (not shown) having sizes matched with the photographingmodes are disposed on a surface of emergence of the third lens unit G₃.

The third embodiment, in which the first lens unit G₁ is to be moved forzooming along loci different between the usual photographing mode andthe panoramic photographing mode, requires exchange of cams orequivalent means in conjunction with a variation of the airspacereserved between the first lens component G_(1A) and the second lenscomponent G_(1B) in the first lens unit G₁. However, the thirdembodiment is advantageous for reducing manufacturing cost of theview-finder optical system since it permits reducing a number of lenselement required to compose the objective lens system by comprising thislens system of two lens unit.

Numerical data for the development diagrams of the optical paths shownin FIG. 14 and FIG. 15 are listed below. Further, aberrationcharacteristics at the wide position, middle position and telephotoposition of the third embodiment in the usual photographing mode thereofare illustrated in FIG. 16, and those at the wide position, middleposition and telephoto position of the optical system in the panoramicphotographing mode are visualized in FIG. 17.

    ______________________________________                                        <Usual photographing mode>                                                    Magnification     0.42˜0.55˜0.73                                  Angle of incidence (2ω)                                                                   49.1°˜37.3°˜27.9°          <Panoramic photographing                                                      mode>                                                                         Magnification     0.50˜0.66˜0.88                                  Angle of incidence (2ω)                                                                   40.6°˜29.1°˜18.9°          Condition (4)     (f.sub.2 + d')/(f.sub.2 + d) = 1.066                        r.sub.1 = -10.9686                                                                        d.sub.1 = 1.000                                                                          n.sub.1 = 1.58423                                                                        ν.sub.1 = 30.49                          r.sub.2 = 7.4301                                                                          d.sub.2 = D.sub.1                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.3 = 14.9945                                                                         d.sub.3 = 2.000                                                                          n.sub.2 = 1.49241                                                                        ν.sub.2 = 57.66                          (aspherical surface)                                                          r.sub.4 = -16.6043                                                                        d.sub.4 = D.sub.2                                                             (variable)                                                        r.sub.5 = 14.9270                                                                         d.sub.5 = 3.500                                                                          n.sub.3 = 1.49241                                                                        ν.sub.3 = 57.66                          r.sub.6 = -20.8791                                                                        d.sub.6 = D.sub.3                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.7 = 21.2950                                                                         d.sub.7 = 20.000                                                                         n.sub.4 = 1.49241                                                                        ν.sub.4 = 57.66                          r.sub.8 = ∞                                                                         d.sub.8 = 1.000                                                   r.sub.9 = ∞                                                                         d.sub.9 = 25.000                                                                         n.sub.5 = 1.49241                                                                        ν.sub.5 = 57.66                          r.sub.10 = ∞                                                                        d.sub.10 = 2.000                                                  r.sub.11 = 17.8960                                                                        d.sub.11 = 3.400                                                                         n.sub.6 = 1.49241                                                                        ν.sub.6 = 57.66                          r.sub.12 = -22.9520                                                                       d.sub.12 = 20.000                                                 (aspherical surface)                                                          r.sub.13 (EP)                                                                 Aspherical surface coefficients                                               Second surface (r.sub.2)                                                      P = 1.0000        A.sub.4 = -0.10232 × 10.sup.-2                        A.sub.6 = -0.87306 × 10.sup.-5                                                            A.sub.8 = 0.57701 × 10.sup.-6                         Third surface (r.sub.3)                                                       P = 1.0000        A.sub.4 = -0.3075 × 10.sup.-3                         A.sub.6  = 0.43923 × 10.sup.-5                                                            A.sub.8 = -0.12541 × 10.sup.-6                        Sixth Surface (r.sub.6)                                                       P = 1.0000        A.sub.4 = 0.87143 × 10.sup.-4                         A.sub.6 = 0.49111 × 10.sup.-6                                                             A.sub.8 = -0.57315 × 10.sup.-8                        Seventh surface (r.sub.7)                                                     P = 1.0000        A.sub.4 = -0.15332 × 10.sup.-3                        A.sub.6 = 0.31536 × 10.sup.-5                                                             A.sub.8 = -0.66269 × 10.sup.-7                        Twelfth surface (r.sub.12 )                                                   P = 1.0000        A.sub.4 = 0.79267 × 10.sup.-4                         A.sub.6 = -0.57040 × 10.sup.-6                                                            A.sub.8 = 0.68501 × 10.sup.-8                         Airspaces at different positions                                              ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        <Usual photographing mode>                                                    Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                               1.0000        1.0000   1.0000                                         D.sub.2                                                                              19.5400       13.5227   8.3699                                         D.sub.3                                                                              10.9600       15.3178  22.1301                                         ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        <Panoramic photographing mode>                                                Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                               2.1511        2.1511   2.1511                                         D.sub.2                                                                              12.1701        6.1524   1.0000                                         D.sub.3                                                                              10.9600       15.3178  22.1301                                         ______________________________________                                    

Fourth Embodiment

FIG. 18 and FIG. 19 are development diagrams illustrating optical pathsat the wide position, middle position and telephoto position of the realimage type variable magnification view-finder optical system preferredas the fourth embodiment of the present invention; FIG. 18 showing theoptical paths in the usual photographing mode and FIG. 19 illustratingthe optical paths in the panoramic photographing mode. This view-finderoptical system consists of an objective lens system 1 and an eyepiecelens system 2. The objective lens system I consists of a first lens unitG₁ which is composed of a first lens component G_(1A) having a positiverefractive power and a second lens component G_(1B) having a negativerefractive power, has a negative refractive power as a whole, and is tobe moved for zooming, a second lens unit G₂ which has a positiverefractive power and is to be moved for zooming, and a third lens unitG₃ composed of a prism which has two reflecting surfaces and a positiverefractive power, whereas the eyepiece lens system 2 consists of afourth lens unit G₄ which is composed of a prism having two reflectingsurfaces and a fifth lens unit G₅ which has a positive refractive powerand is to be moved for zooming. Visual field frames (not shown) havingsizes matched with the photographing modes are disposed on a surface ofemergence of the third lens unit G₃.

The fourth embodiment exhibits an effect to shorten a total length ofthe objective lens system since this embodiment permits moving the firstlens unit G₁ for a distance shorter than that required for moving thefirst lens unit in the third embodiment.

Numerical data for the development diagrams of the optical paths shownin FIG. 18 and FIG. 19 are listed below. Further, aberrationcharacteristics at the wide position, middle position and telephotoposition of the fourth embodiment in the usual photographing modethereof are illustrated in FIG. 20, whereas those at the wide position,middle position and telephoto position of the optical system in thepanoramic photographing mode are visualized in FIG. 21.

    ______________________________________                                        <Usual photographing mode>                                                    Magnification     0.42˜0.55˜0.73                                  Angle of incidence (2ω)                                                                   45.4°˜34.3°˜24.3°          <Panoramic photographing                                                      mode>                                                                         Magnification     0.50˜0.66˜0.88                                  Angle of incidence (2ω)                                                                   40.5°˜30.9°˜22.2°          Condition (4)     (f.sub.2 + d')/(f.sub.2 + d) = 1.066                        r.sub.1 = 185.9539                                                                        d.sub.1 = 3.000                                                                          n.sub.1 = 1.49241                                                                        ν.sub.1 = 57.66                          r.sub.2 = -8.5090                                                                         d.sub.2 = D.sub.1                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.3 = -8.8396                                                                         d.sub.3 = 1.000                                                                          n.sub.2 = 1.58423                                                                        ν.sub.2 = 30.49                          (aspherical surface)                                                          r.sub.4 = 10.9966                                                                         d.sub.4 = D.sub.2                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.5 = 12.3310                                                                         d.sub.5 = 3.500                                                                          n.sub.3 = 1.49241                                                                        ν.sub.3 = 57.66                          r.sub.6 = -13.9658                                                                        d.sub.6 = D.sub.3                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.7 = 11.3161                                                                         d.sub.7 = 15.089                                                                         n.sub.4 = 1.49241                                                                        ν.sub.4 = 57.66                          r.sub.8 = ∞                                                                         d.sub.8 = 1.000                                                   r.sub.9 = ∞                                                                         d.sub.9 = 25.000                                                                         n.sub.5 = 1.49241                                                                        ν.sub.5 = 57.66                          r.sub.10 = ∞                                                                        d.sub.10 = 2.000                                                  r.sub.11 = 17.8960                                                                        d.sub.11 = 3.400                                                                         n.sub.6 = 1.49241                                                                        ν.sub.6 = 57.66                          r.sub.12 = -22.9520                                                                       d.sub.12 = 20.000                                                 (aspherical surface)                                                          r.sub.13 = (EP)                                                               Aspherical surface coefficients                                               Second surface (r.sub.2)                                                      P = 1.0000        A.sub.4 = 0.81532 × 10.sup.-3                         A.sub.6 = -0.77316 × 10.sup.-5                                                            A.sub.8 = 0.98127 × 10.sup.-7                         Fourth surface (r.sub.4)                                                      P = 1.0000        A.sub.4 = -0.65420 × 10.sup.-3                        A.sub. 6 = -0.12246 × 10.sup.-3                                                           A.sub.8 = 0.65356 × 10.sup.-5                         Sixth Surface (r.sub.6)                                                       P = 1.0000        A.sub.4 = 0.18039 × 10.sup.-3                         A.sub.6 = 0.51652 × 10.sup.-5                                                             A.sub.8 = -0.85054 × 10.sup.-7                        Seventh surface (r.sub.7)                                                     P = 1.0000        A.sub.4 = -0.13609 × 10.sup.-3                        A.sub.6 = 0.49750 × 10.sup.-5                                                             A.sub.8 = -0.10119 × 10.sup.-6                        Twelfth surface (r.sub.12)                                                    P = 1.0000        A.sub.4 = 0.79267 × 10.sup.-4                         A.sub.6 = -0.57040 × 10.sup.-6                                                            A.sub.8 = 0.68501 × 10.sup.-8                         Airspaces at different positions                                              ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        <Usual photographing mode>                                                    Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              1.0000        1.0000   1.0000                                          D.sub.2                                                                              11.7890       7.6030   4.0313                                          D.sub.3                                                                              5.8928        9.5264   15.2150                                         ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        <Panoramic photographing mode>                                                Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              2.1672        2.1672   2.1672                                          D.sub.2                                                                              9.9007        5.7250   2.1449                                          D.sub.3                                                                              5.8928        9.5264   15.2150                                         ______________________________________                                    

Fifth Embodiment

FIG. 22 and 23 show development diagrams of optical paths at the wideposition, middle position and telephoto position of the real image typevariable magnification view-finder optical system preferred as the fifthembodiment of the present invention; FIG. 22 showing the optical pathsin the usual photographing mode and FIG. 23 showing the optical paths inthe panoramic photographing mode. In contrast to the first throughfourth embodiments each of which uses the lens unit which is composed oftwo or more lens components and has a negative total focal length, thefifth embodiment adopts a lens unit which is composed of two lenscomponents and has a positive focal length.

The view-finder optical system preferred as the fifth embodimentconsists of an objective lens system 1 and an eyepiece lens system 2.The objective lens system 1 consists of a first fixed lens unit G₁ whichis composed of a first lens component G_(1A) having a negativerefractive power and a second lens component G_(1B) having a positiverefractive power, and has a positive refractive power as a whole, asecond movable lens unit G₂ which has a negative refractive power and ismovable for zooming, a third movable lens unit G₃ which has a positiverefractive power and is movable for zooming, and a fourth lens unit G₄composed of a prism which has two reflecting surfaces and has a positiverefractive power, whereas the eyepiece lens system 2 consists of a fifthlens unit G₅ composed of a prism which has two reflecting surfaces, anda sixth fixed lens unit G₆ having a positive refractive power. Inaddition, visual field frame (not shown) having sizes matched with thephotographing modes are disposed on a surface of emergence of the fourthlens unit G₄.

Even when the first lens unit G₁ is configured so as to have a positivefocal length, the fifth embodiment can provide an effect which issimilar to that obtained by the first embodiment.

Numerical data for the development diagrams of the optical paths shownin FIG. 22 and FIG. 23 are listed below. Further, aberrationcharacteristics at the wide position, middle position and telephotoposition of the fifth embodiment in the usual photographing mode arevisualized in FIG. 24, whereas those at the wide position, middleposition and telephoto position of the optical system in the panoramicphotographing mode are illustrated in FIG. 25.

    ______________________________________                                        <Usual photographing mode>                                                    Magnification     0.40˜0.54˜0.73                                  Angle of incidence (2ω)                                                                   46.2°˜34.1°˜24.9°          <Panoramic photographing                                                      mode>                                                                         Magnification     0.48˜0.65˜0.88                                  Angle of incidence (2ω)                                                                   41.4°˜31.2°˜23.3°          Condition (4)     (f.sub.2 + d')/(f.sub.2 + d) = 1.154                        Condition (5)     m.sub.2T /m.sub.2W - m.sub.3T /m.sub.3W = 0.709             r.sub.1 = ∞                                                                         d.sub.1 = 1.000                                                                          n.sub.1 = 1.58423                                                                        ν.sub.1 = 30.49                          r.sub.2 = 13.5822                                                                         d.sub.2 = D.sub.1                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.3 = 9.7215                                                                          d.sub.3 = 5.000                                                                          n.sub.2 = 1.49241                                                                        ν.sub.2 = 57.66                          (aspherical surface)                                                          r.sub.4 = -25.9373                                                                        d.sub.4 = D.sub.2                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.5 = -11.4264                                                                        d.sub.5 = 1.000                                                                          n.sub.3 = 1.58423                                                                        ν.sub.3  = 30.49                         r.sub.6 = 12.5574                                                                         d.sub.6 = D.sub.3                                                 (aspherical surface)                                                                      (variable)                                                        r.sub.7 = 17.6116                                                                         d.sub.7 = 3.500                                                                          n.sub.4 = 1.49241                                                                        ν.sub.4 = 57.66                          r.sub.8 = -9.5224                                                                         d.sub.8 = D.sub.4                                                 (aspherical surface)                                                          r.sub.9 = 15.3852                                                                         d.sub.9 = 18.026                                                                         n.sub.5 = 1.49241                                                                        ν.sub.5 = 57.66                          r.sub.10 = ∞                                                                        d.sub.10 = 1.000                                                  r.sub.11 = ∞                                                                        d.sub.11 = 25.000                                                                        n.sub.6 = 1.49241                                                                        ν.sub.6 = 57.66                          r.sub.12 = ∞                                                                        d.sub.12 = 2.000                                                  r.sub.13 17.8960                                                                          d.sub.13 = 3.400                                                                         n.sub.7 = 1.49241                                                                        ν.sub.7 = 57.66                          r.sub.14 = -22.9520                                                                       d.sub.14 = 20.000                                                 (aspherical surface)                                                          r.sub.15 (EP)                                                                 Aspherical surface coefficients                                               Second surface (r.sub.2)                                                      P = 1.0000        A.sub.4 = -0.91356 × 10.sup.-4                        A.sub.6 = -0.13485 × 10.sup.-5                                                            A.sub.8 = 0.24772 × 10.sup.-8                         Fourth surface (r.sub.4)                                                      P = 1.0000        A.sub.4 = 0.34207 × 10.sup.-3                         A.sub.6 = -0.12533 × 10.sup.-5                                                            A.sub.8 = 0.12538 × 10.sup.-7                         Sixth Surface (r.sub.6)                                                       P = 1.0000        A.sub.4 = -0.22452 × 10.sup.-3                        A.sub.6 = -0.72786 × 10.sup.-5                                                            A.sub.8 = 0.26251 × 10.sup.-6                         Eighth surface (r.sub.8)                                                      P = 1.0000        A.sub.4 = 0.22498 × 10.sup.-3                         A.sub.6 = 0.25188 × 10.sup.-6                                                             A.sub.8 = 0.62442 × 10.sup.-7                         Fourteenth surface (r.sub.14 )                                                P = 1.0000        A.sub.4 = 0.79267 × 10.sup.-4                         A.sub.6 = -0.57040 × 10.sup.-6                                                            A.sub.8 = 0.68501 × 10.sup.-8                         Airspaces at different positions                                              ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        <Usual photographing mode>                                                    Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              6.4133        6.4133   6.4133                                          D.sub.2                                                                              3.0546        4.1030   9.0351                                          D.sub.3                                                                              9.6123        5.5025   2.7104                                          D.sub.4                                                                              3.4238        6.4852   4.3452                                          ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        <Panoramic photographing mode>                                                Wide angle       Middle   Telephoto                                           position         position position                                            ______________________________________                                        D.sub.1                                                                              3.8060        3.8060   3.8060                                          D.sub.2                                                                              6.0391        7.0876   12.0197                                         D.sub.3                                                                              9.6123        5.5025   2.7104                                          D.sub.4                                                                              3.4238        6.4852   4.3452                                          ______________________________________                                    

In the embodiments of the present invention described above, thereference symbols r₁, r₂, . . . represents radii of curvature on surfaceof the respective lens components, the reference symbols d₁, d₂, . . .designate thicknesses of the respective lens components and airspacesreserved therebetween, the reference symbols n₁, n₂, . . . denoterefractive indices of the respective lens components, and the referencesymbols v₁, v₂, . . . represent Abbe's numbers of the respective lenscomponents.

The aspherical surfaces used in the embodiments of the present inventionhave shapes which are expressed by the following formula using theaspherical surface coefficients described above, and taking a directionof the optical axis as the Z axis and a direction perpendicular to theoptical axis as the Y axis: ##EQU1## wherein the reference symbol Rrepresents a paraxial radius of curvature, the reference symbol Pdesignates a conical coefficient, the reference symbol A₄ denotes anaspherical surface coefficient of the term of the fourth order, thereference symbol A₆ represents an aspherical surface coefficient of theterm of the sixth order, the reference symbol A₈ designates anaspherical surface coefficient of the term of the eighth order and thereference symbol C denotes 1/R.

What is claimed is:
 1. A real image type variable magnificationview-finder optical system comprising:an objective lens systemcomprising a plurality of lens units and having a positive refractivepower as a whole, and an eyepiece lens system for allowing observationof an image formed by said objective lens system; wherein amagnification of said view-finder optical system is changed over anentire zooming range from a wide position to a telephoto positionthereof by varying at least one of airspaces reserved in said pluralityof lens units, wherein at least one of said plurality of lens unitscomprises two or more lens components and wherein a change ofmagnification is performed for switching between a usual photographingmode and a panoramic photographing mode by varying at least one ofairspaces reserved between said two or more lens components.
 2. A realimage type variable magnification view-finder optical system accordingto claim 1 wherein one of said plurality of lens units is used as avari-focal lens unit, and wherein this lens unit comprises a front lenscomponent and a rear lens component, and satisfies the followingcondition where f>0, f₁ <0, and f₂ >0:

    (f.sub.1 +d')/(f.sub.1 +d)>1.02

    [f>0 and f.sub.1 <0, f.sub.2 >0]

    [f<0 and f.sub.1 <0, f.sub.2 <0]

wherein the reference symbol f₁ represents a focal length of the frontlens component, the reference symbol f₂ designates a focal length of therear lens component, the reference symbol f denotes a total focal lengthof said vari-focal lens unit, the reference symbol d represents anairspace reserved between said lens components at a low magnificationlevel, and the reference symbol d¹ designates an airspace reservedbetween said lens components at a high magnification level.
 3. A realimage type variable magnification view-finder optical system accordingto claim 1 wherein one of said plurality of lens units is used as avari-focal lens unit and wherein this lens unit comprises a front lenscomponent and a rear lens component, and satisfies the followingcondition where f>0, f₁ >0, and f₂ <0:

    (f.sub.2 +d')/(f.sub.2 +d)>1.02

    [f>0 and f.sub.1 >0, f.sub.2 <0]

    [f<0 and f.sub.1, 0, f.sub.2 >O]

wherein the reference symbol f₁ represents a focal length of the frontlens component, the reference symbol f₂ designates a focal length of therear lens component, the reference symbol f denotes a total focal lengthof said vari-focal lens unit, the reference symbol d represents anairspace reserved between the lens components at a low magnificationlevel, and the reference symbol d¹ designates an airspace reservedbetween the lens components at a high magnification level.
 4. A realimage type variable magnification view-finder optical system accordingto claim 1 wherein said objective lens system comprises a first fixedlens unit, a second movable lens unit and a third movable lens unit, andwherein said first lens unit comprises a plurality of lens components tobe used for changing a magnification and satisfies the followingcondition:

    m.sub.2T /m.sub.2W -m.sub.3T /m.sub.3W >O

wherein the reference symbol m_(2W) represents a magnification of thesecond lens unit at a wide position of said view-finder optical system,the reference symbol m_(2T) designates a magnification of the secondlens unit at a telephoto position of said view-finder optical system,the reference symbol m_(3W) denotes a magnification of the third lensunit at the wide position of said view-finder optical system and thereference symbol m_(3T) represents a magnification of the third lensunit at the telephoto position of said view-finder optical system.
 5. Areal image type variable magnification view-finder optical systemcomprising:an objective lens system comprising a plurality of lens unitsand having a positive refractive power as a whole, and an eyepiece lenssystem for allowing observation of an image formed by said objectivelens system; wherein a magnification of said view-finder optical systemis changed over an entire zooming range from a wide position to atelephoto position thereof by varying at least one of airspaces reservedin said plurality of lens units, wherein a lens unit disposed on theobject side, out of said plurality of lens units, comprises a positivelens component and a negative lens component, and wherein a change of amagnification for switching between a usual photographing mode and apanoramic photographing mode is performed over an entire zooming rangeby varying an airspace reserved between said positive lens component andsaid negative lens component.
 6. A real image type variablemagnification view-finder optical system comprising:an objective lenssystem comprising a plurality of lens units and having a positiverefractive power as a whole, and an eyepiece lens system for allowingobservation of an image formed by said objective lens system; wherein amagnification of said view-finder optical system is changed over anentire zooming range from a wide position to a telephoto positionthereof by varying at least one of airspaces reserved in said pluralityof lens units, wherein a lens unit disposed on the object side, out ofsaid plurality of lens units, comprises a plurality of lens components,and wherein a change of a magnification for switching between a usualphotographing mode and a panoramic photographing mode is performed overan entire zooming range by varying one or more airspaces reservedbetween said plurality of lens components.
 7. A real image type variablemagnification view-finder optical system according to claim 1 whereinone of said plurality of lens units is used as a vari-focal lens unit,and wherein this lens unit comprises a front lens component and a rearlens component, and satisfies the following condition where f<0, f₁ >0,and f₂ <0:

    (f.sub.1 +d')/(f.sub.1 +d)>1.02

wherein the reference symbol f₁ represents a focal length of the frontlens component, the reference symbol f₂ designates a focal length of therear lens component, the reference symbol f denotes a total focal lengthof said vari-focal lens unit, the reference symbol d represents anairspace reserved between said lens components at a low magnificationlevel, and the reference symbol d¹ designates an airspace reservedbetween said lens components at a high magnification level.
 8. A realimage type variable magnification view-finder optical system accordingto claim 1 wherein one of said plurality of lens units is used as avari-focal lens unit and wherein this lens unit comprises a front lenscomponent and a rear lens component, and satisfies the followingcondition where f<0 and f₁ <0, f₂ >0:

    (f.sub.2 +d')/(f.sub.2 +d)>1.02

wherein the reference symbol f₁ represents a focal length of the frontlens component, the reference symbol f₁ designates a focal length of therear lens component, the reference symbol f denotes a total focal lengthof said vari-focal lens unit, the reference symbol d represents anairspace reserved between the lens components at a low magnificationlevel, and the reference symbol d¹ designates an airspace reservedbetween the lens components at a high magnification level.